Large port equipment such as bridge cranes, portal cranes, and gantry cranes are usually operated in open air near the sea. In recent years, extreme weather like tornadoes and hurricanes frequently occur in coastal areas. A port facility is often subjected to a wind large load due to such extreme weather as well as its large windward area. The port facility, forced by the wind load, moves along its rail in an accelerated manner until it comes to the end of the rail and crashes into a retaining plate at the end of the rail. In this case, a capsizing moment produced by the inertial force is far larger than an anti-capsizing moment produced by the dead weight of the port facility. This usually leads to severe safety accidents such as capsizing of the port facility. In order to prevent port facilities from being moved or blown down by wind when a large wind load is applied thereon, regulations are provided by relevant administrative departments stating that all facilities operated near the sea shall be equipped with safe and reliable anti-slip devices. Anti-slip devices currently used for port facilities mainly include three types: anchor-type, rail braking-type, and rail clamping-type.
An anchor-type anti-slip device is used to fix and limit a port facility in a given place by an anchor and a retaining unit such as support wires. The device is simple in structure and is reliable. However, it is only along the rail that a plurality of anchoring points can be arranged. When a strong wind comes, the port facility has to be moved to anchoring bolts, which is not convenient and it is not always possible to timely stop and anchor the facility, especially in a case of gusty wind.
A rail braking-type anti-slip device is used to enable part of the dead weight of the port facility to be loaded on the top of the rail by using an auxiliary device, thus providing an increased friction between the port facility and the top of the rail for resisting wind. Such a device is simple in structure and convenient to operate, but the increase of the friction can be achieved only through the dead weight of the device. The device has a good anti-slip capability in strong wind, whereas in extreme weather, the wind force is usually far larger than the maximum friction that can be produced by the device; the device is therefore not safe enough.
A rail clamping-type anti-slip device is used to clamp the head of the rail, by way of which a friction is provided, and this friction acts to resist wind. Such a device is advantages in that it can produce a large clamping force and is usually safe and reliable, but limited by the size of the port facility and the installation space, it can merely produce a finite clamping force, and therefore is only suitable for use in common strong wind.
The above three types of anti-slip devices are widely used in various port facilities at present. However, when extreme weather conditions occur, those port facilities are still often turned over or fall into the sea by strong wind due to insufficient capability or malfunction of anti-slip devices thereof. These accidents severely affect normal operations in ports and meanwhile result in economic loss to the ports. It is therefore urgently desirable by the ports to provide a safe and reliable anti-slip device, for addressing the problem that port facilities slide along their rails in extreme weather and are further turned over due to inertial force.